Buffer and Salt Effects in Aqueous Host-Guest Systems: Screening, Competitive Binding, or Both?

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry
• Biochemistry

Background:

• Existing mathematical models for supramolecular chemistry do not account for ion screening.
• Buffers were historically designed without considering their supramolecular properties.
• Uncertainty exists regarding the magnitude of screening effects versus competitive salt/buffer binding.

Purpose of the Study:

• To compare halide affinities using screened and unscreened models.
• To quantify the impact of screening and competitive binding in buffered solutions.
• To provide guidance for supramolecular chemists studying ions in water.

Main Methods:

• Utilized a tetra-cation cavitand to study halide affinities.
• Compared affinity data obtained from a traditional unscreened model and a Debye-Hückel screened model.
• Developed a competitive mathematical model to assess binding attenuation.

Main Results:

• A rule of thumb: consider screening if ionic strength changes by over an order of magnitude.
• Competitive binding by the buffer significantly attenuates host-guest binding.
• For the studied system, competitive binding effects are approximately twice as large as screening effects.

Conclusions:

• For strong binders, competitive complexation is more critical than screening.
• For weaker binders, both screening and competitive complexation must be considered.
• Findings aid in understanding buffer properties and biomacromolecule studies.